Taking advantage of the specificity of a reaction of an enzyme, an enzyme electrode (hereinafter, also referred to as biosensor) has been widely used as a sensor to specifically detect various physiologically active substances. As such an enzyme electrode, one which is constituted such that samples can be analyzed in an electrochemical method or an optical method is widely used. An enzyme electrode for analyzing samples in an electrochemical method usually refers to an electrode in which an enzyme is fixed on the surface of the electrode such as a golden electrode, platinum electrode or carbon electrode. In particular, the enzyme electrode is widely used as a glucose sensor for measuring the concentration of glucose in blood as an important marker in diabetes mellitus.
Although a basic structure of a glucose sensor and a method for manufacturing thereof is well-known, Patent Document 1 discloses a method for manufacturing a special glucose sensor. That is, Patent Document 1 discloses a technique in which the surface of an electrode substrate is modified by forming a cell membrane mimetic structure (phosphatide: 2-methacryloyloxyethyl phosphorylcholine (MPC)) on a support such as an electrode substrate. The shape of the structure of the support is not restricted, and examples thereof include a film, an inner wall of a capillary pipe, a flow channel groove and a particle.
By stabilizing a membrane-associated protein (enzyme or antibody) on the cell membrane mimetic structure layer of the MPC modified surface in a self organized manner, a protein (enzyme or antibody) can be immobilized on the surface of a substrate, a channel wall or a support such that the protein has an orientation.
Such a method described in Patent Document 1 is a method which is, when compared with a variety of conventional methods for immobilizing a protein, different from conventional methods in that in vivo behaviors are mimicked, and a new immobilization method which belongs to a new category which is a sort of a immobilization method by self organization of a protein for itself using any proteins as long as the protein has a membrane association. By this method, an increase in performance of a variety of applications (products) can be attained.
In the above described invention in the prior patent document 1, electron transfer in protein is an extremely effective technique from the viewpoint of immobilizing the orientation of an enzyme. However, in cases where an enzyme electrode is constructed by immobilizing a membrane-associated oxidoreductase, an attempt to attain a high efficiency of electron transfer pathway from the membrane-associated enzyme to the electrode “only by immobilization of enzyme” is described and in the Examples, only a general purpose carbon as a substrate is mentioned, and an approach of improving an ability of giving and receiving an electron in an electrode material used as the substrate was not addressed. An enzyme electrode has room for improvement in that the sensor can be optimized as a sensor which has a high efficiency of manufacturing, a high stability and a high usability because, generally, an enzyme electrode is greatly influenced by a method of manufacturing a substrate electrode or the shape of the electrode in its sensor performance.